Lance Armstrong ended his international career at the Tour Down Under in controversial circumstances, with continued allegations over illegal doping overshadowing his swansong.

The 39-year-old American refused to talk to reporters as he finished his last professional international race 65th overall, almost six minutes adrift of race winner Cameron Meyer of Australia.

Seven-times Tour de France champion Armstrong will now have to deal with a federal investigation in the US triggered by former team mate Floyd Landis's allegations that he and other prominent figures in the sport used performance-enhancing drugs.

The Texan, who never tested positive throughout his career, has denied any wrongdoing and said on Friday he was keen to cooperate with the US Anti-Doping Agency following fresh doping allegations published by Sports Illustrated.

Armstrong, a Team RadioShack rider, is set to make a few international appearances throughout the year but will not be riding as a professional.

Team manager Johan Bruyneel, however, said Armstrong could ride a last pro race in the US at the Tour of California in May.

"@tourdownunder is done. Thanks to everyone for coming out and supporting such a great race. #Adelaide, we're gonna miss ya," he wrote on Twitter after the sixth and final stage.

Reuters